1. Technical Field
The disclosure relates to an operation method for implementing machine-to-machine (M2M) communication in heterogeneous networks, and a gateway and a wireless communication device using the same.
2. Related Art
Currently, the development of a machine-to-machine (M2M) communication system adopts architecture of heterogeneous networks, so as to improve the communication efficiency of the M2M communications application. The M2M communication may also be referred to as machine type communication (MTC). FIG. 1 is a schematic diagram illustrating system deployment of an M2M communication application. As shown in FIG. 1, the M2M communication system 10 includes at least one M2M server 11, at least one M2M user 12, an access network 13, and a plurality of M2M gateways 14a, 14b, . . . , 14n. The M2M server 11 and the M2M user 12 are connected to each other via a communication network and an application program interface (API). The M2M server 11 may be disposed in the access network 13, and may also be disposed in the Internet and is connected to the M2M gateways 14a, 14b, . . . , 14n via the access network 13.
Referring to FIG. 1 again, each of the M2M gateways 14a, 14b, . . . , 14n supports more than two communication protocols at the same time, and is connected to the access network 13 and a local wireless communication network respectively. The local wireless communication network may support IEEE 802.11 standard, IEEE 802.15.4 standard, WiFi standard, bluetooth standard, or ZigBee wireless communication protocol standard (abbreviated as ZigBee hereinafter). The access network 13 may be a wired communication network or wireless access network supporting a power saving mode, so as to decrease a portion of power consumption of the M2M gateways 14a, 14b, . . . , 14n. When the access network 13 is the wireless access network, the access network 13 may support, for example, 3GPP LTE wireless communication standard, IEEE 802.16 standard, or other wireless access network standards. Each of the M2M gateways 14a, 14b, . . . , 14n is connected to M2M nodes via the local wireless communication network, for example, the M2M gateway 14n is connected to a plurality of M2M nodes 15a, 15b, . . . , 15n. The M2M nodes 15a, 15b, . . . , 15n are connected to the M2M server 11 via the M2M gateway 14n serving as an agent, and transmit captured data to the M2M server 11, or receive an instruction message from the M2M server 11. The M2M user 12 may access data of the M2M nodes via the M2M server 11. The access network 13 provides a wide-area communication capability to the M2M gateways 14a, 14b, . . . , 14n, and each of the M2M gateways 14a, 14b, . . . , 14n provides a small-range (or short-distance) communication capability to the served M2M nodes.
However, the access network 13 and the local wireless communication network (for example, a wireless communication network 15) of each of the M2M gateways 14a, 14b, . . . , 14n have different power saving cycles, which are asynchronous in most cases. Two examples are illustrated below through FIG. 2 and FIG. 3. In addition, for the access network 13, the local wireless communication network 15 may also be referred to as a capillary network.
FIG. 2 is a schematic diagram illustrating non-synchronized power saving cycles of heterogeneous networks. To be illustrated more clearly, FIG. 2 shows non-synchronized power saving cycles resulted by mis-alignment between communication windows of an LTE network and a ZigBee network. Referring to FIG. 2, similar to the architecture of heterogeneous networks in FIG. 1, the access network 13 is an LTE network in this case, the M2M server 11 is disposed in the LTE network 13, and the power saving cycle of the LTE network 13 includes two stages: an allowed period and a forbidden period. To be illustrated more clearly, the allowed period follows a periodic or non-periodic tracking area update (TAU), and the forbidden period follows the allowed period. For example, the allowed period follows the TAUs 211, 212, and the occurrence of the TAUs 212, 213 represents the ending of the previous forbidden period. In the allowed period, the LTE network 13 may transmit a signal to the M2M gateway 14n, or receive an uplink signal of the M2M gateway 14n, but in the forbidden period, the LTE network 13 does not process the signal of the M2M gateway 14n. As shown in FIG. 2, signal transmission 251 is processed by the LTE network 13 in the allowed period, but signal transmission 253 occurs in the forbidden period, and thus is not processed. The M2M gateway 14n should wait until the next TAU 212 is received, so as to perform uplink signal transmission or receive downlink signal transmission in the next allowed period.
The wireless communication protocol between the M2M gateway 14n and the M2M node (or referred to as an M2M device) 15n has a power saving cycle different from that of the LTE network 13, and the power saving cycle includes: an active period and a sleep period, which are not completely aligned with the allowed period and the forbidden period of the LTE network 13. The wireless communication network 15 is a ZigBee network in this case, and the M2M device 15n is disposed in the ZigBee network 15. Therefore, as shown in FIG. 2, the downlink signal originally transmitted by the M2M server 11 to the M2M gateway 14n via the signal transmission 251 in the allowed period cannot be transmitted to the M2M device 15n via the signal transmission 252 in the sleep period, thereby generating delay of signal transmission. Likewise, as for the uplink signal transmitted by the M2M device 15n via the signal transmission 254 in the active period, the corresponding LTE network 13 is still in the forbidden period, so the M2M gateway 14n cannot transmit the signal continuously to the M2M server 11 via the signal transmission 253. The M2M gateway 14n should wait until the allowed period after the next TAU 212 to transmit the uplink signal to the M2M server 11, and therefore, the delay of the signal transmission or unnecessary transmission power consumption is generated.
FIG. 3 is a schematic diagram illustrating non-synchronized power saving cycles of heterogeneous networks due to non-periodic signals. To be illustrated more clearly, FIG. 3 shows the non-synchronize power saving cycles of an LTE network and a ZigBee network, where the power saving cycle of the LTE network may be changed due to non-periodic TAU. Referring to FIG. 3, similar to the heterogeneous networks signal transmission in FIG. 2, but a next TAU 312 after a TAU 311 shown in FIG. 3 is a non-periodic TAU (for example, the M2M gateway 14n is handed over to a new tracking area), and occurs earlier than the time point of a next periodic TAU expected by the M2M gateway 14n. Therefore, the power saving cycles that are originally slightly synchronized become non-synchronized now, and the downlink signal originally transmitted by the LTE network 13 via the signal transmission 352 in the allowed period encounters the sleep period of the ZigBee network 15 at the M2M gateway 14n, so the downlink signal cannot be transmitted to the M2M server 11 directly by the M2M gateway 14n. After the non-periodic TAU 312, the M2M gateway 14n may know that it is switched to a new allowed period, and therefore, the uplink signal may be transmitted via signal transmission 352 to the M2M server 11. It is assumed that the M2M gateway 14n does not attempt to synchronize the power saving cycles of the two heterogeneous networks, when the ZigBee network 15 is in the active period, the LTE network 13 is adjusted to the forbidden period due to the non-periodic TAU 312, and if the M2M gateway 14n predicts the allowed period by using the periodic TAU, likewise, the transmission signal 353, after the uplink signal transmission of the signal transmission 354 from the M2M device 15n, cannot be transmitted from the M2M gateway 14n to the M2M server 11 successfully by the LTE network 13 due to the encountered forbidden period.
When the power saving cycles of the wide-area access network 13 and the local wireless communication network are asynchronous, unnecessary transmission power consumption, or even delay of M2M communication, may be resulted. Therefore, how to enable the power saving cycles of heterogeneous networks supporting the M2M communication to be synchronized, is a major issue in this industry.